In conventional magnetic recording disk drives, each read/write head, which includes a magnetoresistive (MR) read head or sensor and an inductive write head, is located on an air-bearing slider that is maintained in close proximity to its associated disk surface as the disks rotate. The MR read sensor and inductive write head are fabricated by deposition and lithographic patterning of a series of thin films on a wafer containing a large number, e.g., 40,000, of rectangular regions arranged in rows, with each region ultimately becoming an individual slider. After formation of the read/write heads at the wafer level, the wafer is cut into bars. The bars are then “lapped” in a plane perpendicular to the wafer surface, with this plane becoming the slider's air-bearing surface (ABS). The bars are then cut into the individual sliders.
The lapping is typically performed as a wet grinding process in which material is removed to reach the ABS. Electrical lapping guides (ELGs) are used to monitor the lapping. Generally, ELGs are formed in the areas of the wafer between the read/write heads. Each ELG includes an electrically conductive structure whose ends are connected to leads that carry current from a control circuit. Each completed MR sensor is a stack of multiple layers and is required to have a precise shape, including a precise track width (TW) and a precise stripe height (SH). The TW is defined during the MR sensor patterning process on the wafer surface, but the SH is defined by the lapping process. The lapping is controlled by monitoring the resistance of the ELGs as material is removed in the grinding process to assure the precise SH of the MR sensor. Thus, a predetermined resistance measurement of the ELG corresponds to the desired MR sensor SH.
Typically the ELG is formed of the same set of multilayered materials and at the same time as the MR sensor to simplify the manufacturing process. Because the ELG and MR sensor are formed of the same materials and in the same process, they will have the same thickness and same electrical resistivity. It is advantageous for the ELG film to have a sheet resistance well matched to the slider fabrication lapping equipment, typically 20-30 Ω/square. Thus the resistivity of the ELG material determines the thickness of the ELG film that will result in such a sheet resistance. Also, because the ELG and MR sensor back edges, i.e., the edges recessed from the lapping surface, are formed at the same time in the same etching step, the ELG and MR sensor back edges will have the same profile if they are made from the same materials and have the same thicknesses. A tapered back edge is desirable for the MR sensor, but results in an unpredictable surface area for the ELG. Because the current through the ELG is in the plane of the ELG this can result in a unpredictable electrical resistance. In order for the back edge of the ELG to be flat, i.e., generally orthogonal to the plane of the ELG film, and thus result in a predictable electrical resistance, the ELG film must be thinner than the sensor stack or have a substantially higher etching rate. To facilitate processing, the ELG film preferably has a thickness substantially similar to or slightly thinner than the sensor stack.
What is needed is a high resistance ELG with an etch rate substantially greater than the etch rate of the stack of layers making up the MR sensor so that a non-tapered flat ELG back edge can be achieved, while providing the needed sheet resistance at a film thickness substantially similar to the thickness of the sensor stack.